A shipping terminal facility for liquefying and shipping a natural gas which is a hydrocarbon gas produced from a wellhead includes: a liquefaction pretreatment facility for performing pretreatment for removing various impurities from the natural gas before liquefaction; and a liquefaction facility for liquefying the natural gas after the pretreatment to provide a liquefied natural gas (LNG).
In the liquefaction pretreatment facility, for example, in order to prevent natural gas blockage in the liquefaction facility, in which the natural gas is cooled to −150° C. or less, removal of water and carbon dioxide is performed, and in addition, for example, removal of hydrogen sulfide is performed.
As an example of the liquefaction pretreatment facility, in Patent Literature 1, there is disclosed a technology involving bringing a natural gas into contact with an amine absorption liquid to absorb and remove hydrogen sulfide or carbon dioxide, followed by allowing the natural gas to flow through an adsorption vessel packed with synthetic zeolite, which is used as a molecular sieve, to adsorb water and the like. The following regeneration operation is performed on the synthetic zeolite at a predetermined time interval: a temperature of the natural gas after the removal of water is increased to from about 230° C. to about 300° C. and then the natural gas is allowed to flow through the adsorption vessel to desorb the adsorbed water and the like.
Meanwhile, in some cases, the natural gas originally contains oxygen or contains oxygen due to air leak from a transport pipe or various devices. Oxygen in the natural gas may cause corrosion in a pipe device involved in the shipping terminal facility or transport equipment, or cause a reduction in treatment efficiency of various impurities in the liquefaction pretreatment facility.
In this regard, the technology disclosed in Patent Literature 1 does not take into consideration, when a natural gas containing oxygen is treated, its influence on the liquefaction pretreatment facility (see the composition of a natural gas to be treated shown in Table 2).
Herein, in Patent Literature 2, there is disclosed a technology involving allowing a natural gas at an atmospheric temperature before being supplied to the liquefaction pretreatment facility to flow through a packed bed of particles obtained by supporting a metal in a reduced state, such as reduced copper, on carrier particles, to thereby remove oxygen. In addition, in Patent Literature 3, there is disclosed a technology for removing oxygen from a landfill gas (gas containing as a main component a methane gas generated in a landfill) or a low-quality natural gas to be transported as a gas, by membrane separation.
However, the technologies disclosed in Patent Literatures 2 and 3 are each a technology for removing, from a natural gas containing oxygen, the contained oxygen, and there is no disclosure of a liquefaction pretreatment facility supposed to treat the natural gas while containing oxygen.